Homogeneous, ductile cobalt based hardfacing foils

ABSTRACT

Hardfacing of metal parts employing a thin, homogeneous, ductile foil is disclosed. The hardfacing foil has a composition consisting essentially of 0 to about 32 atom percent nickel, 0 to about 10 atom percent iron, 0 to about 30 atom percent chromium, 0 to about 2 atom percent tungsten, 0 to about 4 atom percent molybdenum, about 5 to about 25 atom percent boron, 0 to about 15 atom percent silicon and 0 to about 2 atom percent manganese and 0 to 5 atom percent carbon the balance being cobalt and incidental impurities with the proviso that the total of iron, cobalt, nickel, chromium, tungsten and molybdenum ranges from about 70 to 88 atom percent and the total of boron, silicon and carbon ranges from about 12 to 30 atom percent. The ductile foil permits continuous hardfacing of soft matrix, like low carbon and low alloy steels, imparting superior resistance to wear and corrosion.

This application is a continuation of application Ser. No. 285,882 filedJuly 22, 1981, now abandoned.

DESCRIPTION BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to hardfacing of metal parts and, in particular,to a homogeneous, ductile material useful in hardfacing applications.

Hardfacing is a method of depositing a wear and corrosion resistantlayer by melting suitable alloys in-situ. Only the surface of the basemetal being hardfaced is brought to the melting point and the hardfacingrod, wire, or powder is melted and spread over the surface of the basemetal.

Hardfacing is a fast, economical process used to repair or rebuild wornparts, thereby reducing the overall cost of operation and down time. Theprocess can be used to build composite parts, combining hardness,toughness and corrosion resistance at low cost. Suitable wear andcorrosion resistant surface layers can be imparted to parts e.g. diesand forming tools, which are made of cheaper, shock resistant alloyssuch as plain carbon or low alloy steels. Moreover, hardfacing isemployed in structures wherein a soft core is used to overcome stressesand a hard casing is used to resist wear. Examples of such structuresinclude injection and extrusion screws utilized in plastics processingand the like. Many parts, which would otherwise be scrapped, are putback into service for less than their original cost. An additionalsaving is realized because the parts can be rebuilt in-situ whennecessary.

Conventional hardfacing processes include: oxy-acetylene, tungsten inertgas welding (TIG), metal inert gas welding (MIG), submerged arc welddeposition, plasma transferred arc welding and the like. Hardfacingalloys used in such processes contain a substantial amount (about 1 to11 weight percent) of metalloid elements such as boron, silicon orcarbon. Consequently, such alloys are very brittle and are availableonly in rod form or as powder.

One of the most troublesome problems with conventional hardfacingmethods and materials is the difficulty of controlling the thickness anduniformity of the surface layer. The rigid rod-like structures used toadvance hardfacing material to the heating zone cannot be economicallyadapted to continuous surfacing processes. Hardfacing rods are usuallyapplied manually by tungsten inert gas or oxy-acetylene processes whichare non-continuous and inherently slow. Continuous hardfacing has beenachieved by automatic tungsten inert gas machines in which individualrods are fed by gravity, or by plasma transferred arc (PTA) weldingprocedures wherein powdered surfacing material is fed to the heatingzone. Such procedures require materials and equipment that arerelatively expensive. Moreover, the excessive heat generated by theplasma in PTA welding processes adversely affects flowabilitycharacteristics of the hardfacing alloy and dilutes the alloy withmaterial from the base metal, changing the compositional uniformity ofthe surface layer. As a result, there remains a need in the art for aneconomical continuous hardfacing process.

Ductile glassy metal alloys have been disclosed in U.S. Pat. No.3,856,513, issued Dec. 24, 1974 to H. S. Chen et al. These alloysinclude compositions having the formula M_(a) Y_(b) Z_(c), where M is ametal selected from the group consisting of iron, nickel, cobalt,vanadium and chromium, Y is an element selected from the groupconsisting of phosphorus, boron and carbon, and Z is an element selectedfrom the group consisting of aluminum, silicon, tin, germanium, indium,antimony and beryllium, "a" ranges from about 60 to 90 atom percent, "b"ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to15 atom percent. Also disclosed are glassy wires having the formulaT_(i) X_(j), where T is at least one transition metal and X is anelement selected from the group consisting of phosphorus, boron, carbon,aluminum, silicon, tin, germanium, indium, beryllium and antimony, "i"ranges from about 70 to 87 percent and "j" ranges from about 13 to 30atom percent. Such materials are conveniently prepared by rapidquenching from the melt using processing techniques that are nowwell-known in the art. No hardfacing compositions are disclosed therein,however.

There remains a need in the art for a homogeneous, hardfacing materialthat is available in thin, ductile filamentary form.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a homogeneous,ductile hardfacing filament useful as a filler metal for a hardfacedmetal article. The hardfacing filament is composed of metastablematerial having at least 50 percent glassy structure, and has athickness not greater than 0.004 inch (10.16×10⁻³ cm,) and in particulara thickness in the range of 0.0005 to 0.004 inch (1.27×10⁻³ cm to10.16×10⁻³ cm). It has been found that use of hardfacing filament thatis flexible, thin, and homogeneous, as described above, has thepotential of enhancing the speed of hardfacing and enhances the hardnessof the deposited surface layer.

More specifically, the hardfacing filament has a thickness of about0.0005 to 0.004 inch (1.27 cm×10⁻³ to 10.16×10⁻³ cm). Preferably, suchfilament has a composition consisting essentially of 0 to about 32 atompercent nickel, 0 to about 10 atom percent iron, 0 to about 30 atompercent chromium, 0 to about 2 atom percent manganese, 0 to 5 atompercent carbon, and the balance essentially cobalt and incidentalimpurities, with the proviso that the total of iron, cobalt, nickel,chromium, tungsten and molybdenum ranges from about 70 to 88 atompercent and the total of boron, silicon and carbon ranges from about 12to 30 atom percent.

The homogeneous hardfacing filament of the invention is fabricated by aprocess which comprises forming a melt of the composition and quenchingthe melt on a rotating quench wheel at a rate of at least about 10⁵ °C./sec.

The filler metal filament is easily fabricable as, homogeneous, ductileribbon, which is useful for hardfacing. Further, the homogeneous,ductile hardfacing filament of the invention can reduce the depositthickness resulting in less dilution from the substrate and less cost ingrinding of the deposited layer.

The invention will be more fully understood and further advantages willbecome apparent when reference is made to the following detaileddescription of the preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention a homogeneous ductile hardfacingfilamentory material in foil form is provided. The hardfacing foil isless than 0.004 inch (10.16×10⁻³ cm) thick, preferably about 0.004 to0.002 inch (10.16×10⁻³ to 5.08×10⁻³ cm) thick and has a compositionconsisting essentially of 0 to about 32 atom percent nickel, 0 to about10 atom percent iron, 0 to about 30 atom percent chromium, 0 to about 2atom percent tungsten, 0 to about 4 atom percent molybdenum, about 2 toabout 25 atom percent boron, 0 to about 15 atom percent silicon and 0 toabout 2 atom percent manganese and 0 to 5 atom percent carbon, thebalance being cobalt and incidental impurities with proviso that thetotal of iron, cobalt, nickel, chromium, tungsten and molybdenum rangesfrom about 70 to 88 atom percent and the total of boron, silicon andcarbon ranges from about 12 to 30 atom percent.

These compositions are suitable for hardfacing low carbon and low alloysteels with greater resistance to wear and corrosion.

By homogeneous is meant that the foil, as produced, is of substantiallyuniform composition in all dimensions. By ductile is meant that the foilcan be bent to a round radius as small as ten times the foil thicknesswithout fracture.

Examples of hardfacing alloy compositions within the scope of presentinvention are set forth in Table 1 below.

                                      TABLE I                                     __________________________________________________________________________                    Co Cr Ni Fe                                                                              B  Si Mo Mn W C                                    __________________________________________________________________________    Co--Ni--Fe--B--Si                                                                         at %                                                                              39.4                                                                             -- 30.9                                                                             6.9                                                                             9.8                                                                              13 -- -- --                                                                              --                                               wt %                                                                              46.5                                                                             -- 36.3                                                                             7.8                                                                             2.1                                                                              7.2                                                                              -- -- --                                                                              --                                   Co--Fe--B--Si                                                                             at %                                                                              70.3                                                                             -- -- 5.7                                                                             8  16 -- -- --                                                                              --                                               wt %                                                                              82.9                                                                             -- -- 6.4                                                                             1.7                                                                              9  -- -- --                                                                              --                                   Co--Ni--Fe--B--Si--                                                                       at %                                                                              43.8                                                                             -- 21.9                                                                             7.3                                                                             13.0                                                                             12.0                                                                             2.0                                                                              -- --                                                                              --                                   Mo          wt %                                                                              52.2                                                                             -- 26.0                                                                             8.3                                                                             2.8                                                                              6.8                                                                              3.9                                                                              -- --                                                                              --                                   Co--Fe--B--Si--Mo                                                                         at %                                                                              65.2                                                                             -- -- 5.3                                                                             12.5                                                                             13.0                                                                             4.0                                                                              -- --                                                                              --                                               wt %                                                                              76.5                                                                             -- -- 5.9                                                                             2.7                                                                              7.3                                                                              7.6                                                                              -- --                                                                              --                                   Co--Cr--Fe-- Ni--B--                                                                      at %                                                                              48.4                                                                             26.3                                                                             2.5                                                                              2.6                                                                             11.7                                                                             1.7                                                                              -- 1.3                                                                              1.0                                                                             4.5                                  Si--Mn--W--C                                                                              wt %                                                                              55.8                                                                             28.0                                                                             3.0                                                                              3.0                                                                             2.6                                                                              1.0                                                                              -- 1.5                                                                              4.0                                                                             1.1                                  Co--Cr--B--Si--W                                                                          at %                                                                              62.9                                                                             21.2                                                                             -- --                                                                              11.6                                                                             3.0                                                                              -- -- 1.3                                                                             --                                               wt %                                                                              70.5                                                                             21.0                                                                             -- --                                                                              2.4                                                                              1.6                                                                              -- -- 4.5                                                                             --                                   __________________________________________________________________________

The hardfacing foils of the invention are prepared by cooling a melt ofthe desired composition at a rate of at least about 10⁵ ° C./sec,employing metal alloy quenching techniques well-known to the glassymetal alloy art; see, e.g., U.S. Pat. Nos. 3,856,513 and 4,148,973. Thepurity of all compositions is that found in normal commercial practice.

A variety of techniques are available for fabricating continuous ribbon,wire, sheet, etc. Typically, a particular composition is selected,powders or granules of the requisite elements in the desired portionsare melted and homogenized, and the molten alloy is rapidly quenched ona chill surface, such as a rapidly rotating metal cylinder.

Under these quenching conditions, a metastable, homogeneous, ductilematerial is obtained. The metastable material may be glassy, in whichcase there is no long range order. X-ray diffraction patterns of glassymetal alloys show only a diffuse halo, similar to that observed forinorganic oxide glasses. Such glassy alloys must be at least 50% glassyto be sufficiently ductile to permit subsequent handling, such asstamping complex shapes from ribbons of the alloys. Preferably, theglassy metal alloys must be at least 80% glassy, and most preferablysubstantially (or totally) glassy, to attain superior ductility.

The metastable phase may also be a solid solution of the constituentelements. In the case of the alloys of the invention, such metastable,solid solution phases are not ordinarily produced under conventionalprocessing techniques employed in the art of fabricating crystallinealloys. X-ray diffraction patterns of the solid solution alloys show thesharp diffraction peaks characteristic of crystalline alloys, with somebroadening of the peaks due to desired fine-grained size ofcrystallites. Such metastable materials are also ductile when producedunder the conditions described above.

Hardfacing of metal substrates is readily accomplished in accordancewith the invention by feeding a continuous filament from a spool orother similar wound supply source to a heating zone. The filament so fedis homogeneous and ductile, composed of metastable material having atleast 50 percent glassy structure and has a composition consistingessentially of 0 to about 32 atom percent nickel, 0 to about 10 atompercent iron 0 to about 30 atom percent chromium, 0 to about 2 atompercent tungsten, 0 to about 4 atom percent molybdenum, about 2 to about25 atom percent boron, 0 to about 15 atom percent silicon and 0 to about2 atom percent manganese, 0 to 5 atom percent carbon, the balance beingcobalt plus incidental impurities with the proviso that the total ofiron, cobalt, nickel, chromium, tungsten and molybdenum ranges fromabout 70 to 88 atom percent and the total of boron, silicon and carbonranges from about 12 to 30 atom percent. Heat is applied to the filamentwithin the heating zone to melt the filament and cause it to becomedeposited on a work surface in close proximity thereto. The work surfaceis then permitted to cool, causing the deposited filament to form ahard, adherent coating thereon.

Use of the hardfacing process of the present invention affordssignificant advantages. A thin (0.002"), dense coating can be depositedon the metal substrate. Oxide content in the coating is lower than thatgenerally produced by flame spraying operations. A superior bond betweenthe coating and the substrate is attained by the diffusion of metalloidelements from the coating into the substrate. Hardfacing can be carriedout in a furnace or with a torch, with the result that the need forspecialized equipment is eliminated.

The following examples are presented to provide a more completeunderstanding of the invention. The specific techniques, conditions,materials, proportions and reported data set forth to illustrate theprinciples and practice of the invention are exemplary and should not beconstrued as limiting the scope of the invention.

EXAMPLES Example 1

Ribbons about 2.5 to 25.4 mm (about 0.10 to 1.00 inch) wide and about 13to 60 m (about 0.0005 to 0.0025 inch) thick were formed by squirting amelt of the particular composition by overpressure of argon onto arapidly rotating copper chill wheel (surface speed about 3000 to 6000ft/min or 914.4 to 1828.8 m/min). Metastable, homogeneous ribbons ofsubstantially glassy alloys having the following compositions in weightpercent and atom percent were produced. The compositions of the ribbonsare set forth in Table II below.

                                      TABLE II                                    __________________________________________________________________________                    Co Cr Ni Fe                                                                              B  Si Mo Mn W C                                    __________________________________________________________________________    Co--Ni--Fe--B--Si                                                                         at %                                                                              39.4                                                                             -- 30.9                                                                             6.9                                                                             9.8                                                                              13 -- -- --                                                                              --                                               wt %                                                                              46.5                                                                             -- 36.3                                                                             7.8                                                                             2.1                                                                              7.2                                                                              -- -- --                                                                              --                                   Co--Fe--B--Si                                                                             at %                                                                              70.3                                                                             -- -- 5.7                                                                             8  16 -- -- --                                                                              --                                               wt %                                                                              82.9                                                                             -- -- 6.4                                                                             1.7                                                                              9  -- -- --                                                                              --                                   Co--Ni--Fe--B--Si--                                                                       at %                                                                              43.8                                                                             -- 21.9                                                                             7.3                                                                             13.0                                                                             12.0                                                                             2.0                                                                              -- --                                                                              --                                   Mo          wt %                                                                              52.2                                                                             -- 26.0                                                                             8.3                                                                             2.8                                                                              6.8                                                                              3.9                                                                              -- --                                                                              --                                   Co--Fe--B--Si--Mo                                                                         at %                                                                              65.2                                                                             -- -- 5.3                                                                             12.5                                                                             13.0                                                                             4.0                                                                              -- --                                                                              --                                               wt %                                                                              76.5                                                                             -- -- 5.9                                                                             2.7                                                                              7.3                                                                              7.6                                                                              -- --                                                                              --                                   Co--Cr--Fe--Ni-- B--                                                                      at %                                                                              48.4                                                                             26.3                                                                              2.5                                                                             2.6                                                                             11.7                                                                             1.7                                                                              -- 1.3                                                                              1.0                                                                             4.5                                  Si--Mn--W--C                                                                              wt %                                                                              55.8                                                                             28.0                                                                              3.0                                                                             3.0                                                                             2.6                                                                              1.0                                                                              -- 1.5                                                                              4.0                                                                             1.1                                  Co--Cr--B--Si--W                                                                          at %                                                                              62.9                                                                             21.2                                                                             -- --                                                                              11.6                                                                             3.0                                                                              -- -- 1.3                                                                             --                                               wt %                                                                              70.5                                                                             21.0                                                                             -- --                                                                              2.4                                                                              1.6                                                                              -- -- 4.5                                                                             --                                   __________________________________________________________________________

Ribbons of different alloy compositions were used to develop ahardfacing layer in accordance with the following procedure. The ribbonthickness varied from 0.001"-0.0025" (2.54×10⁻³ to 6.35×10⁻³ cm). Theribbons were positioned relative to AISI 304 stainless steel sheets(about 0.0625" [1.59×10⁻¹ cm] thick) and the composites were heatedseparately to a temperature of 1900°-2300° F. (1038°-1260° C.) varyingfrom alloy to alloy in a vacuum furnace to about 15 minutes. The sampleswere then removed from the furnace, sectioned, mounted, and polished formicrohardness measurement of the hardfaced layer.

The composition and Knoop hardness values (100 gms load, 15 sec.indentation time) of each ribbon alloy tested are set forth in TableIII.

                  TABLE III                                                       ______________________________________                                        Sample                          KHN                                           No.   Composition (at %)        100                                           ______________________________________                                        1     Co.sub.39.4 Ni.sub.30.9 Fe.sub.6.9 B.sub.9.8 Si.sub.13                                                  133                                           2     Co.sub.70.3 Fe.sub.5.7 B.sub.8 Si.sub.16                                                                257                                           3     Co.sub.43.8 Ni.sub.21.9 Fe.sub.7.3 B.sub.13 Si.sub.12 Mo.sub.2                                          222                                           4     Co.sub.65.2 Fe.sub.5.3 B.sub.12.5 Si.sub.13 Mo.sub.4                                                    240                                           5     Co.sub.48.4 Cr.sub.26.3 Ni.sub.2.5 Fe.sub.2.6 B.sub.11.7 Si.sub.1.7           Mo.sub.1.3 W.sub.1.0 C.sub.4.5                                                                          186                                           ______________________________________                                    

Having thus described the invention in rather full detail it will beunderstood that these details need not be strictly adhered to but thatvarious changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the present invention asdefined by the subjoined claims.

What is claimed is:
 1. A hardfaced metal article, said article havingbeen hardfaced with a homogeneous, ductile hardfacing foil composed ofmetastable material having at least 50 percent glassy structure and acomposition consisting essentially of 0 to about 30.9 atom percentnickel, 0 to about 7.3 atom percent iron, 0 to about 26.3 atom percentchromium, 0 to about 1.3 atom percent tungsten, 0 to about 4 atompercent molybdenum, about 8 to about 13 atom percent boron, 1.7 to about13 atom percent silicon, 0 to about 1.3 atom percent manganese, 0 to 4.5atom percent carbon, and 39.4 to 70.3 atom percent cobalt plusincidental impurities with the proviso that the total of iron, cobalt,nickel, chromium, tungsten and molybdenum ranges from about 70 to 88atom percent and the total of boron, silicon and carbon ranges fromabout 12 to 30 atom percent.